This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        ACK acknowledgment        BS base station        C-PDU control-protocol data unit        D2D device-to-device        DL downlink (eNB towards UE)        E2E end-to-end        eNB E-UTRAN Node B (evolved Node B)        EPC evolved packet core        E-UTRAN evolved UTRAN (LTE)        FDD frequency division duplex        FDM frequency division multiplex        HARQ hybrid autonomous retransmission request        IMTA international mobile telecommunications association        ITU-R international telecommunication union-radiocommunication sector        LTE long term evolution of UTRAN (E-UTRAN)        LTE-A LTE advanced        MAC medium access control (part of layer 2, L2)        MM/MME mobility management/mobility management entity        NACK negative acknowledgment        NodeB base station        OFDM orthogonal frequency division multiplex        O&M operations and maintenance        PCCH physical control channel        PDCCH physical downlink control channel        PDCP packet data convergence protocol        PHY physical (layer 1, L1)        PUCCH physical uplink control channel        Rel release        RL radio link        RLC radio link control        RRC radio resource control        RRM radio resource management        SGW serving gateway        SC-FDMA single carrier, frequency division multiple access        TCP transmission control protocol        TDD time division duplex        TDM time division multiplex        TPC transmission power control        UDP user datagram protocol        UE user equipment, such as a mobile station, mobile node or mobile terminal        UL uplink (UE towards eNB)        UPE user plane entity        UTRAN universal terrestrial radio access network        One modern communication system is known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA). In this system, the DL access technique is OFDMA, and the UL access technique is SC-FDMA.        
One specification of interest is 3GPP TS 36.300, V8.11.0 (2009-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8), incorporated by reference herein in its entirety. This system may be referred to for convenience as LTE Rel-8. In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Release 8 LTE system. More recently, Release 9 versions of at least some of these specifications have been published including 3GPP TS 36.300, V9.3.0 (2010-03).
FIG. 1 of this Application reproduces a figure taken from a reference, namely, FIG. 4-1 of 3GPP TS 36.300 V8.11.0, and shows the overall architecture of the EUTRAN system (Rel-8). The E-UTRAN system includes eNBs, providing the E-UTRAN user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UEs. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME by means of a S1 MME interface and to a S-GW by means of a S1 interface (MME/S-GW 4). The S1 interface supports a many-to-many relationship between MMEs/S-GWs/UPEs and eNBs.
Of particular interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10 and beyond Rel-10) targeted towards future IMTA systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). Reference in this regard may be made to 3GPP TR 36.913, V9.0.0 (2009-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 9). Reference can also be made to 3GPP TR 36.912 V9.2.0 (March 2010) Technical Report 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Feasibility study for Further Advancements for E-UTRA (LTE-Advanced) (Release 9).
A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is directed toward extending and optimizing the 3GPP LTE Rel-8 radio access technologies to provide higher data rates at lower cost. LTE-A will be a more optimized radio system fulfilling the ITU-R requirements for IMT-Advanced while keeping the backward compatibility with LTE Rel-8.
Integration of new network topologies into cellular networks such as those described above is gaining more attention and interest, both in the telecommunications industry and in telecommunications research. Good examples are, e.g., a current study item of heterogeneous networks in LTE/LTE-A of 3GPP. Such heterogeneous networks include a deployment of macros, micros, picos, femtos and relays in the same spectrum. One step further is to enable heterogeneous local communication directly among devices and machines under supervision of the network. Heterogeneous in a local domain could include the following:                Network controlled device-to-device (D2D) communication including communication in clusters of devices;        (Semi-)Autonomous D2D communication in a cellular network;        A grid/group of local machines communicating with each other while performing certain tasks in co-operative way;        An advanced cellular device acting as a gateway for a number of low-capability devices or machines to allow these to access a cellular network; and        Co-operative downloading or multicasting within a cluster of devices.        
Such local communication schemes may play a remarkable role in the future. For instance, there are estimates that there will be 50 billion devices with wide varieties of capabilities connected to networks by 2020. D2D communication, in particular, is attracting significant interest for at least the following reasons:                D2D is seen as a potential technique for improve local area coverage;        D2D is seen as a potential solution to improve resource efficiency;        D2D can aid in conserving both UE and eNB transmit (Tx) power;        D2D can aid in reducing the load on the cellular network; and        D2D has the potential to provide new types of services for end users.        
Nonetheless, there are certain situations in which D2D communications could be improved.